1. Field of the Invention
The present invention relates to user-programmable interconnect architectures. More particularly, the present invention relates to FPGA architectures including direct interconnections between internal logic function circuits and I/O modules on the integrated circuit.
2. The Prior Art
User-programmable interconnect architectures are known in the art. A particular species of user-programmable interconnect architecture is known as a field programmable gate array (FPGA) and includes a plurality of logic function circuits disposed in an array on the integrated circuit. The logic function circuits have inputs and at least one output and are usually programmable, allowing them to be defined to perform one of several combinatorial or sequential logic functions. A plurality of I/O modules is disposed on the integrated circuit, usually at or near the periphery of the array. The I/O modules comprise input and output buffers connected to I/O pads of the integrated circuit and act as an interface for routing signals onto and off of the integrated circuit. The output buffers are usually equipped with control inputs which may be used to place their outputs in a high impedance state when the I/O pad to which they are connected is used as an input pad.
A matrix of general interconnect conductors is superimposed on the array of logic function circuits and the I/O modules. Individual ones of the general interconnect conductors are connectable to the I/O module interface and to the inputs and outputs of the logic function modules using user-programmable interconnect elements, which may be, for example, transistors, non-volatile transistor elements, antifuses, or the like. By programming selected ones of the user-programmable interconnect elements, the FPGA integrated circuit can be customized to perform a user-specified function.
While the existing FPGA architectures have proved to be useful and have gained wide acceptance, they suffer from several drawbacks. First, the connections between the I/O modules and the logic function circuits must be made using programmable elements, which add a delay to the signal path. In addition, the I/O module adds another level of logic beyond the logic function circuits.